Polyesters formed of saturated acids, ethylene glycol or propylene glycol and 1,4-butanediol are widely used in industry as starting materials in the preparation of polyurethanes. Such polyesters are ordinarily made in batch processes wherein the acid, the glycol and the diol are brought together simultaneously under conditions suitable for condensation polymerization to take place. Polyesters thus prepared show varying degrees of color formation, which is undesirable in most instances because the color may be carried over into the polyurethane product.
It has now been found, according to the present invention, that color formation in such a polyester can be significantly reduced if the polyester is prepared by first forming a reaction mass of the acid and the glycol and then adding the butanediol to the mass when the acid-glycol reaction is practically complete.